Objectives

The primary objective of the DASH-Sodium Trial was to test the effects of two dietary patterns and three sodium intake levels on blood pressure in adult men and women with blood pressure higher than optimal or at stage 1 hypertension (systolic 120-159 mm Hg and diastolic 80-95 mm Hg).

Background

Blood pressure is an established risk factor for stroke and heart disease, and research has shown this risk to increase across the full range of blood pressure levels. The DASH study established that a diet emphasizing fruits, vegetables, whole grains, poultry, fish and low-fat dairy products can reduce systolic blood pressure by an average of 5.5 mm Hg and diastolic blood pressure by 3 mm Hg. Coupling the DASH diet with reduced sodium intake may potentially reduce blood pressure levels even further. Approximately 48% of adults have blood pressure above optimum levels, but below stage 2 hypertension (systolic blood pressure 120-159 mm Hg or diastolic pressure 80-95 mm Hg), and the DASH diet along with reduced sodium intake could provide suitable levels of control for a large segment of the population. To examine the effect of the DASH diet along with reduced sodium intake on blood pressure, two dietary patterns (a control diet typical of what many Americans consume and the DASH diet) were compared at three levels of sodium intake: (1) higher level comparable to current US intake, (2) an intermediate level which mirrors the upper limit of current recommendations, and (3) a lower intake which could lower blood pressure even more.

Design

Four clinical centers and a coordinating center participated in the trial. Participants took part in a two week run-in period in which they were fed the higher sodium control diet. After the run-in period, participants were randomly assigned to one of the two diets using a parallel-group design and were fed each of the sodium levels for 30 consecutive days using a randomized crossover design. DASH - sodium was an outpatient feeding study, and study staff prepared all meals and snacks in research kitchens. To be eligible, participants had to be age 22 years or older, with diastolic blood pressure 80-95 mm Hg, systolic blood pressure 120-160 mm Hg, and free of anti-hypertensive medications or medications that would affect blood pressure. A total of 412 participants were randomized, and approximately 60% were African-American and 59% were women. Recruitment began in 1997 and all diets were completed in 1999.

Conclusions

Compared to the higher sodium control diet, the DASH diet reduced systolic blood pressure by an average of 5.9, 7.2, and 8.9 mm Hg for the higher, intermediate and lower sodium intakes respectively. Diastolic blood pressure was reduced by 2.9, 3.5, and 4.5 mm Hg for the higher, intermediate, and lower sodium intake levels. Reducing sodium intake in the control diet from higher to intermediate levels reduced systolic blood pressure by an average of 2.1 mm Hg and by 6.7 mm Hg to the lower sodium intake. Reducing sodium intakes to the lower level resulted in significantly lower systolic blood pressure in all sex, race, and hypertension status subgroups with the exception of non-black participants without hypertension. (N Engl J Med 2001;344:3-10).

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